The invention relates to automatic liquid control valves to control liquid flows in many different types of applications, the present invention being particularly related to controlling liquid flows in water supplies and hydrocarbon pipelines.
Automatic control valves have many different applications, such as controlling pressure downstream from the valve, controlling levels in tanks or reservoirs either upstream or downstream from the valve, reducing undesirable effects of pressure surges in supplies due to actuating related valves or pumps, etc. The valves used in this wide range of applications are modulating or throttling valves which throttle flow through the valve to attain a desired pressure drop or flow condition across the valve. Throttling of flow is attained by positioning a main valve member with respect to a complementary valve seat to control size of clearance through the valve, if necessary by essentially continuously varying position of the valve member with respect to the seat. A liquid filled, variable volume control chamber is sealed with a movable partition means, for example a piston with a sliding resilient seal, or a flat or rolling flexible diaphragm, the partition means being coupled to the main valve member to position the valve member in response to pressure within the control chamber. Most of the valves used for these purposes are controlled automatically by use of a pilot pressure system, in which a pilot circuit senses pressures in the flow on an upstream and/or downstream side of the valve, or at some other convenient location depending on the application, for example at the base of a reservoir in which reservoir depth is to be controlled. The pilot system generates at least one type of pressure signal which is processed following conventional techniques and generates a control signal which is fed into the control chamber used to control position of the main valve member.
The sliding piston seals or the flat or rolling diaphragms used to isolate the control chamber from the main flow through the valve are subject to eventual failure due to movement and aging. Failure causes liquid loss from the control chamber, which usually causes the control valve itself to fail "open", that is, the main valve member moves to the full position, which causes flow through the valve to increase, with consequent problems arising upstream or downstream depending on the application of the valve. Because the sliding seals or diaphragm are contained within the valve itself and are not visible from the outside, inspection of the seals or diaphragm without dismantling the valve is usually impossible, and thus there is a tendency to replace the seals or diaphragm prematurely rather than risk failure in normal use. Also, the pilot control systems used to control the valves can fail, for example, due to blockage of a conduit with dirt, or failure of the pilot control valve to control properly, and thus in very critical areas preventative maintenance costs can be considerable.
Some valves are designed to fail "closed" and are termed "fail-safe" valves. While the failure of these valves can prevent damage in some applications, when they fail there is a complete cessation of flow through the valve, which in other applications can aggravate dangerous situations. Other valves use a parallel duplicate or redundant system in which both systems have some duplicating components which are operative simultaneously, and thus are both are subject to wear, usually at the same rate, and thus are likely to fail at approximately similar moments in time.
U.S. Pat. No. 1,199,567 in which the inventors are Kellogg and Crowell, and U.S. Pat. No. 3,762,436 in which the inventor is Clayton, both disclose liquid pressure regulating valves using diaphragms. U.S. Pat. No. 1,157,957, in which the inventor is Phau, also discloses a liquid pressure regulator to control in pressure in storage reservoirs. U.S. Pat. No. 3,930,518, in which the inventors are Fuller and Smith, discloses a valve which is responsive to a differential pressure switch to operate a valve closing system. U.S. Pat. No. 2,523,826, in which the inventor is Henzelman, discloses a back pressure regulator valve, and U.S. Pat. No. 2,329,323, in which the inventor Benz, discloses a ratio regulator for liquified gases and volatile liquids using a pair of diaphragms cooperating with a common shaft. While some of the patents above disclose valves which are for use in similar applications to the present invention, none of them shows a independent backup system which is normally inoperative and therefore not subject to wear, and is only brought into operation upon detection of critical or undesirable flow conditions and, when brought into operation, clearly maintains the desired flow condition.